The present invention is directed to processing of synthetic yarn to develop bulk in the yarn by crimping and shrinking the yarn through the application of heat and moisture to the yarn when in a relaxed condition. The development of bulk in yarn is desired where increased coverage of the yarn in fabrics is beneficial, as in clothing and especially in carpets. A fully bulked yarn will provide softness and coverage in carpets with a lesser amount of yarn than when non-bulked or only partially bulked yarn is used.
Conventionally, yarn is bulked by steaming the yarn in relaxed skeins, or in stuffer boxes, by feeding the yarn through crimping rollers, by conveying the yarn in an air jet that causes the yarn to bulk when the air jet is dissipated into the atmosphere or against a baffle, or by passing the yarn through a heating chamber in a somewhat relaxed condition. However, none of these conventional processes provide optimum bulking as the yarn is not fully relaxed and in some instances is not subjected to heat and moisture for a sufficient period to allow full bulk development. Further, in the case of skein handling, which is the most common bulking process, the yarn is not uniformly relaxed with the result that non-uniform bulking occurs, producing detectable streaks in fabrics, such as carpet, made from the yarn.
By the present invention, yarn is handled in a continuous process with the yarn being substantially completely relaxed in haphazardly curled condition while heat and moisture are applied for substantially complete bulk development, and the bulked yarn is discharged in fully relaxed condition for subsequent treatment without further direct handling that could reduce the bulk before heat-setting or other treatment. Thus, the present invention obtains optimum and uniform bulking of yarn to an extent that is not attainable by any previously known process, and does so in a simple and reliable manner and at high production rates.